Chemical Equations

Skeleton Equations

Chemical changes are usually modeled through chemical equations, showing how atoms break apart and rearrange themselves using Chemical Symbols. For example:

Reactants are on the left side (they do the reacting) while products are on the right side (they are produced by the reaction)

Any equation that does not have coefficients on it is known as a skeleton equation. Just like energy, matter cannot be created nor destroyed, just rearranged (though nuclear processes complicate this a bit). Since nothing is destroyed we must balance the equations we write. This means the reactant side of a chemical equation must have the same types atoms as the product side:

4 Hydrogen total and 2 Oxygen total are on both sides of the chemical equation here!

Coefficients (numbers in front of the molecule) are added to the equation to balance an equation out. If there is a subscript, the coefficient multiplies the subscript for the total number of that type of atom in that molecule and the total number of each type of atom on each side of the reaction must be the same.

One method for going from skeleton equations to balanced equations is to determine how much of each element you have on each side of the equation then to use multiplication to even them out. The other easy way to do balancing is to use pictures or models to help visualize what's going on.

There are some extra processes that can help out when trying to balance things:

Start with the elements in the least amount of places first-usually the more difficult ones will fall into place.
When balancing polyatomics, keeping them together as a single unit can often save time. If doing this, remember that water can also be H and OH combined.
If something looks like it'd need a fraction to fully balance the equation, put that fraction there then multiply everything in the equation by the denominator to make it all whole numbers.

Polyatomic Ions

Some groups of atoms also form common ions together! These are known as polyatomic ions (poly means many). When using polyatomics and balancing charges, the entire polyatomic goes in parenthesis if more than one is needed.

States of Matter in Chemical Equations

When a solid is dissolved into water its state of matter is known as aqueous. Most substances that readily dissolve in water are highly polar since water itself is very polar. The substances break apart into individual ions or smaller particles and float around being attracted to the water. Many of these are also electrolytes, substances that are usually ionic and conduct electricity when dissolved. The most common electrolyte is table salt, where Na+ and Cl- are in the solution, making it so for every NaCl atom 2 ions get dissolved.

Chemical equations also often include state symbols, showing if a chemical is in the solid (s), liquid (l), gaseous (g), or aqueous (aq) phase. State symbols are not generally necessary for the balancing process and do not change how to balance equations.

When ionic solids, acids, and other polar materials enter water the highly polar hydrogen bonds of water break these substances apart into their individual cation and anion pieces. These ions move around and collide into any other ions that have been dissolved in the water, giving them the ability to interact since they are all moving freely within the water more than they would in solid form.

Ionic Chemical Equations

We can break chemical equations down further into their individual ions to better see if a precipitation reaction happens. If we do so we create a complete ionic equation. For example:

AgNO3 (aq) + NaCl (aq) would become Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq)

Looking at our four dissolved ions, Ag and Cl form a solid, so the complete ionic equation becomes:

Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) -> AgCl (s) + Na+ (aq) + NO3- (aq)

Since the NO3- and Na+ are not a part of the actual reaction they are known as spectator ions. We can remove the spectator ions from our complete ionic equation to make the net ionic equation:

Ag+ (aq) + Cl- (aq) -> AgCl (s)

Additional Resources

Balancing Equations Practice Video

Interesting Links

How Sugar is Made

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